This invention relates to a drive apparatus for the auxiliary equipment of a motor, and more particularly but not exclusively to the case in which the motor is the engine of an automobile.
In an automobile, engine auxiliary equipment such as charging generators, water pumps, air conditioning compressors, and oil pumps for hydraulic servo steering is belt-driven by a drive pulley mounted on the end of the crankshaft of the engine. This auxiliary equipment is generally designed to be operated at low speeds, and if driven at the same speed as the engine when the engine is running at high speeds, the operation of the equipment would produce considerable power losses. Therefore, means are generally provided for adjusting the rotational speed of the drive pulley for the auxiliary equipment with respect to the rotational speed of the engine so that the auxiliary equipment can be operated at suitable speeds.
FIG. 1 shows one type of auxiliary equipment drive apparatus which has been proposed in the past. In this apparatus, a rotating input member in the form of a hollow input shaft 1 is directly connected to the crankshaft of an unillustrated engine. A rotating output member in the form of a pulley 2 is rotatably supported on the input shaft 1 and on a stationary plate 3. The pulley 2 comprises a peripheral casing 2a and an end plate 2b which is secured to the casing 2a by screws 2c. The pulley 2 drives a number of pieces of unillustrated auxiliary equipment by belts which are wound around the pulley casing 2a. The end plate 2b is rotatably supported by the input shaft 1 through a ball bearing 4, while the peripheral casing 2a is rotatably supported by the stationary plate 3 through another ball bearing 5. The stationary plate 3 is secured to a stationary portion of the engine by unillustrated bolts which pass through bolt holes 3a formed in the stationary plate 3. A roller bearing 6 is provided between the input shaft 1 and a flange portion of the stationary plate 3 which surrounds the input shaft 1.
Between the input shaft 1 and the peripheral casing 2a of the pulley 2 is an adjustable, stepless, frictional speed change mechanism in the form of a planetary cone reduction gear 7 which transmits drive force from the input shaft 1 to the pulley 2 at an adjustable speed. The planetary cone reduction gear 7 has a plurality of planetary cones 8 which are rotatably mounted by their stems on a cone support ring 9 which surrounds the input shaft 1 and can rotate with respect thereto. Each of the cones 8 has a first frictional transmission surface 8a which forms the top surface of the cone 8, a second frictional transmission surface 8b which forms the base of the cone 8, and a third frictional transmission surface 8c which forms the periphery of the stem of the cone 8. The axis of each cone 8 is sloped with respect to the axis of the input shaft 1 so that a line which is parallel to the axis of the input shaft 1 can be drawn from the vertex of the cone 8 to its base along its top surface. The first frictinal transmission surface 8a of each cone 8 frictionally engages with the inner surface of a speed change ring 10 which is concentrically disposed with respect to the input shaft 1. The speed change ring 10 has a plurality of pins 10a secured to its outer surface, and on each of these pins 10a are rotatably mounted two roller keys 10b and 10c. The outer roller keys 10b are disposed inside corresponding axially-extending grooves 2d formed in the inner surface of the peripheral casing 2a of the pulley 2. With this structure, the rotation of the speed change ring 10 is transmitted to the peripheral casing 2a of the pulley 2 by the outer roller keys 10b, causing the pulley 2 to rotate at the same speed as the speed change ring 10, but at the same time, the speed change ring 10 is able to freely move in the axial direction of the pulley 2. The second frictional transmission surface 8b of each cone 8 is in frictional engagement with the outer periphery of an input ring 11 which surrounds the input shaft 1. The input ring 11 is caused to rotate together with the input shaft 1 by a transmission mechanism 12 comprising a first race 12a and a plurality of balls 12b. The balls 12b are held between the undulating surface of the first race 12a and a similar undulating surface of a second race which is formed on the inner portion of the input ring 11. When the iput shaft 1 is rotated, the transmission mechanism 12 exerts a torque on the input ring 11 as well as a force in the axial direction which causes the outer end of the input ring 11 to contact with the second frictional transmission surface 8b of each of the planetary cones 8. The third frictional transmission surface 8c of each planetary cone 8 is in frictional engagement with the outer peripheral surface of a stationary guide ring 13 which is secured to the stationary plate 3. When the planetary cones 8 are caused to rotate about their axes by the rotation of the input ring 11, the frictional engagement between the guide ring 13 and the third frictional transmission surfaces 8c causes the planetary cones 8 to revolve about the axis of the input shaft 1. A roller bearing 14 is disposed between the guide ring 13 and the input shaft 1.
The reduction ratio of the reduction gear 7 can be adjusted by moving the speed change ring 10 in the axial direction of the input shaft 1, and this is accomplished by a reduction ratio adjustment mechanism in the form of an overcurrent electromagnetic brake 15 and a cylindrical cam 16. The overcurrent electromagnetic brake 15 has an electromagnetic coil 15a which is mounted on the stationary plate 3 and which uses the stationary plate 3 as a portion of a magnetic path, an electromagnetic pole 15b which is also secured to the stationary plate 3, and a cylindrical overcurrent cup 15c which surrounds the pole 15b and which is made of a material with good electrical conductivity. The cylindrical cam 16 is a tubular member having a flange 16a which is integral with the overcurrent cup 15c and a plurality of axially-extending cam surfaces 16b which confront the inner roller keys 10c mounted on the pins 10a of the speed change ring 10. The cylindrical cam 16 and the overcurrent cup 15c are rotatably supported by the pulley casing 2a through a ball bearing 17. A number of packing rings 18 are disposed between the input shaft 1, the pulley 2, and the stationary plate 3 so as to prevent lubricating oil from leaking from the inside of the pulley 2.
A pulse pickup 20 is mounted on the stationary plate 3 so as to confront one end of the pulley casing 2a across a small gap. The portion of the pulley casing 2a which it confronts has a plurality of slits 2e cut in it at regular intervals around its circumference. When the pulley casing 2a rotates, the pulse pickup 20 produces an electrical output signal in the form of an electrical pulse each time one of the slits 2e passes by it.
The mechanism for adjusting the reduction ratio of the planetary cone reduction gear 7 is controlled by a control circuit shown in the form of a block diagram in FIG. 2. Element number 21 is a waveform shaping circuit which receives the output signal from the pulse pickup 20 and which produces a waveform-shaped output signal. Element number 22 is a digital-to-analog converter which receives the output signal from the waveform shaping circuit 21, which is a periodic digital signal which is proportional to the rotational speed of the pulley 2, and converts it into an analog output signal. Element number 23 is a load detecting circuit which produces output signals indicative of the load conditions of the engine and of the various pieces of auxiliary equipment which are driven by the drive apparatus. Element number 24 is a calculating circuit which receives the output signals from the load detecting circuit 23, computes the optimal rotational speed of the pulley 2 based on the load conditions, and produces a corresponding output signal. Element number 25 is a comparator which compares the output signals from the digital-to-analog converter 22 and from the calculating circuit 24 and produces a corresponding output signal. Element number 26 is a current control circuit which duty controls the exciting current of the electromagnetic coil 15a of the overcurrent electromagnetic brake 15 based on the output signal from the comparator 25.
The operation of this conventional drive apparatus is as follows. When the input shaft 1 is rotated by the unillustrated engine, the input ring 11 is caused to rotate by the transmission mechanism 12, and the planetary cones 8 are caused to rotate about their axes. At the same time, due to the frictional engagement between the planetary cones 8 and the stationary guide ring 13, the planetary cones 8 revolve about the input shaft 1, performing planetary motion. The frictional engagement between the planetary cones 8 and the speed change ring 10 causes the speed change ring 10 to rotate about the center of the input shaft 1, and this rotation is transmitted to the pulley casing 2a by the outer roller keys 10b. The pulley 2 thus rotates at the same speed as the speed change ring 10, and the unillustrated auxiliary equipment is belt-driven by the pulley 2.
The reduction ratio of the reduction gear 7 can be set at a desired value by moving the speed change ring 10 in the axial direction of the input shaft 1, and this is done by controlling the damping force exerted by the overcurrent electromagnetic brake 15. When the speed change ring 10 rotates, rotational force is transmitted to the cam surfaces 16b of the cylindrical cam 16 by the inner roller keys 10c, and this causes the cylindrical cam 16 and the overcurrent cap 15c to rotate as a single body at the same speed as the speed change ring 10. When the electromagnetic coil 15a of the overcurrent electromagnetic brake 15 is excited, a damping force is exerted on the overcurrent cup 15c, and this causes the cam surfaces 16b to press against the inner roller keys 10c, and a longitudinally-directed cam force is exerted on the speed change ring 10 through the inner roller keys 10c. This force acts to move the speed change ring 10 in the axial direction of the input shaft 1. At the same time, in a planetary cone reduction gear of this type, the planetary motion of the planetary cones 8 produces a longitudinally-directed biasing force on the speed change ring 10. In this conventional mechanism, the cam surfaces 16b are shaped such that the longitudinally-directed force which is exerted on the speed change ring 10 by the overcurrent electromagnetic brake 15 through the cam surfaces 16b is opposite in direction to the biasing force on the speed change ring 10 produced by the planetary motion. Therefore, when a damping force is applied to the overcurrent cup 15c, the speed change ring 10 will move to the point on the top surfaces of the planetary cones 8 where the longitudinally-directed force exerted on it by the cam surfaces 16b is balanced by the biasing force. By adjusting the damping force exerted on the overcurrent cup 15c, the speed change ring 10 can be moved to any desired position along the top surfaces of the planetary cones 8. The damping force produced by the overcurrent electromagnetic brake 15 is automatically controlled by the control circuit illustrated in FIG. 2, which automatically adjusts the exciting current of the electromagnetic coil 15a based on operating condition..
Although the operation of this conventional drive apparatus is quite satisfactory, it has the problem that it requires a pulse pickup 20 to detect the rotational speed of the pulley 2, and this increases the weight and the cost of the apparatus. Furthermore, the requirement that slits 2e be provided in the pulley casing 2a increases manufacturing costs. In addition, there is the disadvantage that the pulley casing 2a must be made of a magnetic material, limiting the range of materials which can be employed.